The LiPo balancer cell acts like a big and very accurate zener diode; when the cell voltage is under a threshold fixed by the user the system is in “idle state” and watch only for the voltage with a equivalent resistance of some KOhm and a negligible current shunt. When the voltage reaches the threshold the balancer element will start to shunt current from the cell with an internal power resistor. [via]
LiPo Balancer – [Link]
In this project there are actually 3 chargers combined in a single PCB, each charger having an output voltage of 4.2V. You can cascade them to become charger fit for 2 or 3 cels Lipo pack. The transformer used is 3 x 8 VAC. As more and more devices are powered with LiPo batteries such a charger could come handy some day.
DIY LiPo Charger - [Link]
Here is the simple Lithium Ion Battery Charger. Lithium Ion batteries pack a lot of power by weight compared to other types. There are 2 things that need to be handled differently than nicad on NiMH 1. They cannot be used as a direct substitute (even if they look like other AA’s) since they run at about 3.6 (or so) volts.2. They cannot be charged in the same way as nicad or NiMH. [via]
Lithium Ion Battery Charger – [Link]
An appliance of some kind is in technical terms a load – it draws power. We can simulate this using a device, a dummy load, that draws power at a known rate. Dummy loads are usually nothing more than a large resistor. The supply voltage is dropped across the resistor and the energy contained in the supply current is dumped as heat – often an awful lot of heat! [via]
ELV Dummy Load for Power Supply Testing - [Link]
NiMH cells are still very popular energy source in portable media like digital cameras, clocks, various players, etc. They provide quite good energy density for reasonable price. Charging current of NiMH cells should be about 10% of their rated hourly capacity. And charging time should not exceed 14 hours. Following charger is what it does. [via]
AVR based NiMH charger - [Link]
A new bunch of Cornell University student projects 2008 have shown up. One of the projects is a device that is capable to measure various AC power parameters in real time. These include:
- Real power
- Apparent power
- Power factor
- RMS Voltage
- RMS Current
- Energy usage (Kilowatt-Hours)
Embedded systems that are dealing with DAC require a good voltage references. Despite all voltage references have their nominal values there are specific tolerances that indicates how much values can vary from nominal value. References as a rule are semiconductors that characteristics are effected by temperature.
For instance if we decide to use a 2.5V voltage reference then (zener) diode LM336A-2.5 may be a good choice for this.
Voltage references in embedded design - [Link]
Portable USB charger’s will always be handy, lets face it these days every gadget around us has USB charging capabilities. This is a very basic and simple project, and cheap too. Maybe its time for you to build your own diy portable USB charger.
DIY portable USB charger - [Link]
Any USB port can supply 5V at up to 500mA. The USB standard specifies that a device may not use more than 100mA until it has negotiated the right to use 500mA, but apparently no USB ports enforce that requirement. This makes the USB port a convenient source of power for devices such as this charger. [via]
USB AA NiMH and NiCd Battery Charger - [Link]
A flyback converter implements a current-limited power supply to charge lead-acid batteries. The MAX773 current-mode controller limits the output current and the flyback transformer provides isolation and flexibility for input voltages both above and below the battery voltage. The MAX471 current-sense amplifier monitors the charging current and feeds back to a threshold detector so that below a designed threshold the flyback converter can switch to a lower charging voltage for trickle-charge mode. [via]
MAX773 Lead Acid Batteries Charger - [Link]